JP2000021011A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately conduct the feedback control of the output of a semiconductor laser in the optical pickup device having a light source unit. SOLUTION: A semiconductor substrate 11 having a substrate surface 111, on which a monitoring light receiving element 25 is formed, is incorporated in the package of the light source unit of an optical pickup device. A semiconductor laser 2 is placed on the surface 111 of the substrate 11 through a submount 24. The element 25 is arranged on the frontal position of a front emitting end face 2f of the laser 2. A portion Lf1 of front laser beams Lf emitted from the face 2f is directly made incident on the element 25. Since a portion of the beams Lf is directly detected by the element 25, accurate control is conducted for the objective output of the front laser beam output. Moreover, a portion of the light beams is led to the element 25, no additional optical element such as a reflection plate is required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup device having a light source unit in which a semiconductor laser, a light receiving element for signal reproduction and a light receiving element for monitoring are incorporated in a common package.

[0002]

2. Description of the Related Art An optical pickup device used for recording / reproducing an optical disk such as a CD, DVD, MO, etc.
2. Description of the Related Art There is known a light source unit having a configuration in which a semiconductor laser, a light receiving element for signal reproduction, and a light receiving element for monitoring are incorporated in the same package. Such an optical pickup device is disclosed, for example, in Japanese Patent Application Laid-Open No. 3-278330.

In an optical pickup device disclosed in Japanese Patent Application Laid-Open No. 3-278330, a hologram element and an objective lens are arranged in this order from a semiconductor laser toward an optical disk. Further, an objective lens, a hologram element, and a reflection mirror are arranged in this order from the optical disk toward the light-receiving element for signal reproduction.

In this optical pickup device, a semiconductor laser is mounted on a semiconductor substrate fixed to a heat sink, and these are integrated as a light source unit. In this light source unit, a sub heat sink is mounted on a semiconductor substrate, a semiconductor laser is mounted on the upper surface, and a laser beam is emitted in a direction parallel to the substrate surface of the semiconductor substrate.
A light receiving element (for signal reproduction) is formed behind the semiconductor laser on the substrate surface of the semiconductor substrate, and a reflection mirror is arranged above the light receiving element. In addition to the light-receiving element for signal reproduction, a monitoring light-receiving element for feedback-controlling the laser light output of the semiconductor laser is formed behind the semiconductor laser.

[0005] In this optical pickup device, laser light (forward laser light) emitted from the front emission end face of the semiconductor laser is transmitted through the hologram element and then focused on the optical disk via the objective lens. The return light from the optical disc is diffracted by the hologram element, then falls by the reflection mirror, and is guided to the light receiving element for signal reproduction.
Signal reproduction, tracking error detection and focus error detection are performed according to the detection result of the light receiving element.

In this type of optical pickup device, a part of the laser light (rearward laser light) emitted from the rear emission end face of the semiconductor laser directly irradiates a monitor light receiving element formed on the surface of the semiconductor substrate. I do. Based on the detection result of the monitoring light receiving element, feedback control is performed so that the output of the forward laser light of the semiconductor laser becomes constant.

[0007]

In the optical pickup device having the above configuration, the output of the front laser light is indirectly feedback-controlled based on the output of the rear laser light. Since the indirect feedback control is performed as described above, the actual output of the forward laser beam varies.

[0008] CD-R, DVD-ROM, DVD-R,
For optical discs such as MD and PD,
Laser light output during recording (about 10 times the laser light output during reproduction)
Output). For this reason, when the output of the forward laser beam varies as described above and the laser beam output deviates from the optical output range suitable for the optical disc to be recorded, a problem such as distortion of the shape of the write pit occurs. At the time of reproduction, if the laser beam output becomes too large, data recorded on the optical disc may be erased.

Here, it is conceivable to guide a part of the forward laser light to the monitor light-receiving element using a reflector or the like.
A new optical element such as a reflector is required. When a new optical element is required, the cost of the light source unit increases,
Also, it takes time to assemble the elements.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to control the output of a forward laser beam from a semiconductor laser to an output suitable for recording or reproduction on an optical disk without requiring a new optical element. To provide an optical pickup device including a light source unit capable of performing the above.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a semiconductor laser and a laser beam for reproducing a signal and a tracking error detecting device, the laser beam being emitted from a front emission end face of the semiconductor laser. A separating element for separating the laser light into light, a focusing means for focusing the laser light for signal reproduction and the laser light for tracking error detection on the optical recording medium, and a signal reproduction for detecting return light from the optical recording medium A light receiving element for monitoring, a light receiving element for monitoring for feedback control of an output of a forward laser light emitted from the semiconductor laser, and a light guide system for guiding the return light to the light receiving element for signal reproduction. , The semiconductor laser,
The light-receiving element for signal reproduction and the light-receiving element for monitoring are incorporated in a common package and integrated as a light source unit, and the light guide system diffracts and separates the return light from the forward laser light from the semiconductor laser. In the optical pickup device including the diffraction element, the light source unit has a semiconductor substrate having a substrate surface in which the monitor light receiving element is formed in the package, and the monitor light receiving element is the semiconductor laser. And a part of the front laser beam is directly incident on the monitor light receiving element.

In the optical pickup device of the present invention, part of the forward laser light emitted from the semiconductor laser is directly detected by monitoring light detection, and the output of the forward laser light is feedback-controlled based on the detection result. . Since a part of the control target is detected in this manner, the output of the forward laser beam is set to an output suitable for recording / reproducing on the optical recording medium.
The output of the forward laser light can be controlled. Further, since the forward laser light is used for feedback control, the backward laser light is unnecessary. For this reason, by increasing the reflectance at the rear emission end face of the semiconductor laser, the laser light can be intensively emitted from the front emission end face of the semiconductor laser. This makes it possible to generate a high-output front laser beam required for recording on the optical recording medium with a small driving current.

Further, since a part of the forward laser light is directly detected by the monitoring light receiving element, an optical element for guiding a part of the laser light to the monitoring light receiving element is unnecessary.
Therefore, it is possible to prevent an increase in the cost of the light source unit and a complicated operation for assembling the optical element.

The signal reproducing light receiving element may be formed on a substrate surface of the semiconductor substrate on which the monitor light receiving element is formed. In this case, if the optical path length from the semiconductor laser to the diffractive element is equal to the optical path length from the diffractive element to the signal reproducing light receiving element, the optical path length of the return light is smaller than that in the related art. Since it can be shortened, the optical system of the optical pickup device can be made compact.

It is preferable that the semiconductor laser is mounted on an upper surface of a heat sink provided on the substrate surface of the semiconductor substrate on which the monitor light receiving element is formed. With this configuration, the heat sink can efficiently dissipate the heat of the semiconductor laser.

Here, in the optical pickup device of the present invention, it is desirable to detect the focus error of the focusing means using the tracking error detecting laser light. In this case, a diffraction element having only a simple optical path separation function can be adopted as a diffraction element for diffracting and separating return light from the optical recording medium. In such a diffraction element, the diffraction pattern can be simplified. For example, a linear diffraction pattern can be used. The diffraction element having such a diffraction pattern can reduce the deterioration of the diffraction characteristics due to the wavelength fluctuation of the forward laser light emitted from the semiconductor laser, the displacement of the mounting position of each optical element, and the like. Thereby, the operation of the optical pickup device can be stabilized. In addition, since a simplified diffraction pattern may be produced, the tolerance for the production error of the diffraction pattern can be increased, and the production cost of the diffraction element can be reduced.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

(Overall Configuration of Optical Pickup Device) FIG. 1 is a schematic configuration diagram of an optical system of the optical pickup device. The optical pickup device 1 includes a semiconductor laser light source 2A including a semiconductor laser 2 and a heat sink 24, and a front laser light Lf emitted from a front emission end face 2f of the semiconductor laser 2.
A first diffraction element 13 for separating the laser light for signal reproduction and the laser light for tracking error detection, and the laser light for signal reproduction and the laser light for tracking error detection separated by the first diffraction element 13. A rising mirror 18 for raising, an objective lens 12 for condensing each laser beam raised by the mirror 18 on the optical disk 4, and a light-receiving element 3 for signal reproduction for detecting the return light Lr from the optical disk 4. And a light guide system 50 for guiding the return light Lr to the light receiving element 3 for signal reproduction.

The light guide system 50 includes a second diffraction element 14 for diffracting and separating the return light Lr from the optical disk 4 from a forward laser light Lf from the semiconductor laser 2, and the second diffraction element 1.
And a reflection mirror 15 for reflecting the light diffracted by 4 toward the signal reproducing light receiving element 3.

In the optical pickup device 1 of this embodiment, the semiconductor laser light source 2A, the light receiving element 3 for signal reproduction, the light guide system 50 and the first diffraction element 13 are incorporated in a common package 20 and integrated as a light source unit 10. Have been.

(Structure of Light Source Unit) FIGS. 2 and 3 show the light source unit. FIG. 2A is a plan view of the light source unit, and FIGS. 2B and 2C are FIGS.
It is sectional drawing in the AA 'line of (A), and sectional drawing in the BB' line. FIG. 3 is a front view of the light source unit as viewed from the front (the direction of arrow C in FIG. 2A). In FIG. 2A, a part of the package is omitted for easy understanding of the internal configuration of the light source unit. In the following description, the width direction of the package is described as an X direction, the vertical direction of the package is defined as a Y direction, and the front-rear direction of the package is defined as a Z direction.

As shown in these figures, the light source unit 1
The package 20 has a flat rectangular parallelepiped shape. Inside the package 20, a semiconductor substrate 11, a heat sink 24 installed on a substrate surface 111 of the semiconductor substrate 11, and a top surface of the heat sink 24 are mounted. A semiconductor laser 2 is provided, and a signal reproducing light receiving element 3 and a monitoring light receiving element 25 formed on the substrate surface 111 of the semiconductor substrate 11 are provided. The package 20 includes a reflection mirror 15, first and second diffraction elements 13 and 1,
4 is attached.

On the front surface 204 of the package 20, there is formed a cylindrical projection 201 which projects vertically toward the front.
A light passage hole 203 is formed by the cylindrical projection 201, and the first and second diffraction elements 13 and 14 are attached thereto. The forward laser light Lf emitted from the semiconductor laser 2 is emitted to the outside via these elements 13 and 14, and the return light Lr from the optical disc 4 is guided to the inside of the package 20.

The package 20 comprises a substantially square package main body 21 whose upper part is open, and a package lid plate 22 which covers this upper opening. The package body 21 and the package cover plate 22 define a chamber 202 in which the semiconductor substrate 11 and the semiconductor laser light source 2A are mounted, and also form a cylindrical projection 201. The package body 21 and the package cover plate 22 are both molded products.

FIG. 4 (A) is a plan view of the package body, and FIGS. 4 (B) and 4 (C) are D-D in FIG. 4 (A), respectively.
It is sectional drawing in the D 'line, and sectional drawing in the EE' line. As shown in these figures, the package body 21
Has a substantially rectangular bottom wall 211, a front wall 212, a rear wall 213, and left and right side walls 214 and 215 rising from four sides of the bottom wall 211. Front wall 21
2 is cut in a concave shape, and a pair of left and right protruding side walls 216 and 217 extend perpendicularly to the front wall 212 from both sides thereof. The lower ends of these protruding side walls 216, 217 are connected by a protruding bottom wall 218 extending forward from the bottom wall 211. The protruding side walls 216 and 217 and the protruding bottom wall 218 form an extension 219 protruding forward.

The width of the extension 219 is smaller than the width of the package body 21, and the extension 219 is
1 is formed at a position offset from the center in the width direction.

The surface of the bottom wall 211 of the package body 21 is flat and serves as a reference plane 30 for defining the positions of the semiconductor laser light source 2A and the semiconductor substrate 11. A rectangular plate-shaped stage 231 of the lead frame 23 is fixed to the reference surface 30. Lead of lead frame 23 (12 leads in this example) 23
2 has a pad portion located on the reference surface 30, and a portion serving as an external connection terminal extends through the rear wall 213 of the package body 21 to the outside. These external connection terminal portions are arranged at regular intervals in the width direction of the package.

(Structure of the semiconductor substrate and its peripheral portion)
FIG. 5 is an enlarged perspective view showing a semiconductor substrate and its peripheral portion, and FIG. 6 is a plan view showing a substrate surface of the semiconductor substrate. As shown in FIGS. 2, 5, and 6, the semiconductor substrate 11 is bonded to the stage 231 of the lead frame 23 with a silver paste. Semiconductor substrate 11
On one side of the substrate surface 111 in the width direction,
A substantially rectangular electrode portion 111a long in the front-rear direction is formed, and a signal processing circuit 26 is formed on the other side.
The electrode portion 111a is located at a position offset toward the rear side. A heat sink 24 is fixed on the electrode portion 111a with a silver paste. The heat sink 24 is a metal plate having a constant thickness and excellent heat radiation characteristics. The semiconductor laser 2 is fixed on the upper surface of the heat sink 24 with a silver paste. The heat of the semiconductor laser 2 is absorbed by the heat sink 24 and emitted to the outside.

The semiconductor laser 2 has a front emission end face 2f from which the front laser light Lf is emitted. From the front emission end face 2f, a front laser beam Lf is emitted forward toward a direction parallel to the substrate surface 111 of the semiconductor substrate 11. The emission point of the forward laser light Lf of the semiconductor laser 2 is located substantially at the center in the vertical direction of the package 20 on the front emission end face 2f, and the forward laser light Lf emitted therefrom.
Are the first and second attached to the light passage hole 203.
Are emitted to the outside through the diffraction elements 13 and 14 of FIG.

On the substrate surface 111 of the semiconductor substrate 11,
Signal processing circuit 2 formed on the side of electrode section 111a
Reference numeral 6 increases the level of the output signal of the light-receiving element 3 for signal reproduction, and generates a pit signal (RF signal), a tracking error signal (TE signal), and a focus error signal (FE signal) by an external control device. This is a circuit to make it easier. The signal reproducing light receiving element 3 is formed in front of the signal processing circuit 26. Therefore, the signal reproducing light receiving element 3
Is formed at a position in front of the front emission end face 2f of the semiconductor laser 2 and at a position laterally deviated from the optical axis Lu of the front laser beam Lf.

A monitor light receiving element 25 is formed at a position on the substrate surface 111 of the semiconductor substrate 11 in front of the front emission end face 2f of the semiconductor laser 2. Semiconductor laser 2
A part Lf1 of the front laser light Lf emitted from the front emission end face 2f of the light emitting device directly enters the monitoring light receiving element 25.

Here, the front emission surface 2f of the semiconductor laser 2
And the lateral position of the signal reproducing light-receiving element 3 is a position that easily becomes a dead space. In this example, the monitoring light receiving element 25 is formed at this position. That is, on the substrate surface 111 of the semiconductor substrate 11,
The light receiving element 3 for signal reproduction, the light receiving element 25 for monitoring, the signal processing circuit 26, and the like are formed in an optimally arranged state, and the area on the substrate surface 111 is effectively used.

The light receiving element 25 for monitoring is the semiconductor laser 2
Is not arranged in front of the front emission end face 2f, the part Lf1 of the front laser light Lf is reflected on the substrate surface 111, then reflected inside the package 20 and enters the signal reproducing light receiving element 3. There is fear. Forward laser light Lf
Is incident on the light receiving element 3, the output signal of the light receiving element 3 contains noise. In this example, since the monitoring light receiving element 25 is formed at this position, noise is included in the output signal of the light receiving element 3 due to a part Lf1 of the forward laser light Lf being incident on the light receiving element 3. It will not be lost.

(Configuration of Signal Reproducing Light-Receiving Element) FIG. 7 shows the signal reproducing light-receiving element 3 in an enlarged manner. As shown in this figure, the signal receiving light-receiving element 3 has seven light-receiving surfaces A, B1, and B that are elongated in the width direction of the package 20.
2, C, D1, D2, and E. The light receiving surface A is for detecting a pit signal (RF signal), and the remaining light receiving surfaces are for detecting a tracking error signal (TE signal) and a focus error signal (FE signal). In the light-receiving element 3 for signal reproduction, the remaining light-receiving surfaces are arranged three by three in the front-rear direction with the light-receiving surface A as a center. A light receiving surface B1, a light receiving surface C and a light receiving surface B2 are arranged in this order in front of the light receiving surface A, and a light receiving surface D1, a light receiving surface E and a light receiving surface D2 are arranged in this order behind the light receiving surface A. I have. The amounts of light received on these light receiving surfaces are converted into electric signals and supplied to the signal processing circuit 26. Note that the tracking error signal (TE
The method of generating the focus error signal (FE signal) and the focus error signal (FE signal) will be described later.

The signal processing circuit 26 amplifies the electric signal supplied from each light-receiving surface and converts the signal into a voltage corresponding to the amount of received light, and appropriately calculates a signal obtained by the I / V amplifier. It is composed of an arithmetic circuit section and the like. The output of the signal processing circuit 26 is applied to the substrate surface 11 of the semiconductor substrate 11.
Each of the electrodes 111b is taken out from each electrode 111b.

Each electrode 111b is electrically connected to a predetermined lead pad of the lead frame 23 by wire bonding (see FIG. 2). Further, an electrode (not shown) formed on the semiconductor laser 2 is also electrically connected to a predetermined pad portion of the lead 232 by wire bonding. An output signal from each of the electrodes 111b is guided to a control device (not shown) arranged outside the light source unit 10 via the lead frame 23, and an RF signal, a TE signal, and an FE signal are generated.

The light receiving surface of the monitoring light receiving element 25 formed on the substrate surface 111 of the semiconductor substrate 11 has an electrode 11
1c is formed. This electrode 111c is
Similarly to 11b, it is electrically connected to the corresponding pad portion of the lead 232 by wire bonding. The output signal from the electrode 111c is guided to the control device via the lead frame 23, where feedback control of the laser light output of the semiconductor laser 2 is performed.

(Mounting Position of Each Optical Element) Referring to FIG. 2, in the light source unit 10, the reflecting mirror 15, the first diffractive element 13, and the second diffractive element are located at predetermined positions of the package 20. Element 14 is mounted.

Each of the first and second diffraction elements 13 and 14 has a rectangular shape. The first diffraction element 13 is connected to the bottom wall 211 and the extension 21 of the package body 21.
9 and is fixed by an adhesive or the like.
The second diffraction element 14 is fixed to the front surface of the extension 219 by an adhesive or the like.

The reflection mirror 15 has a rectangular shape. A mirror mounting portion 221 is formed integrally with the package lid plate 22 at a portion of the package lid plate 22 closing the upper opening of the package main body 21 at a position almost directly above the signal reproducing light receiving element 3. The mirror mounting portion 221 is a protrusion having a trapezoidal cross section formed from almost directly above the light receiving element 3 for signal reproduction toward the rear. The front surface of the mirror mounting portion 221 is a mirror mounting surface 222 inclined forward by 45 degrees, on which the reflection mirror 15 is fixed by an adhesive or the like.

The return light Lr from the optical disk 4 which enters the package via the first and second diffraction elements 13 and 14 hits the reflection mirror 15 and falls down at a right angle by this mirror 15 to receive light for signal reproduction. Irradiate 3.

(Basic operation of optical pickup device)
The basic operation of the optical pickup device will be described with reference to FIG. In the light source unit 10, the semiconductor laser light source 2
Forward laser light Lf emitted from the semiconductor laser 2 of A
Are incident on the first diffraction element 13 almost perpendicularly.
The first diffraction element 13 has a diffraction grating surface (not shown). This diffraction grating surface has a function of dividing the forward laser light Lf that has entered substantially perpendicularly into a main beam and two sub beams. In addition, the optical disc 4 has a function of converting the wavefronts of the two sub beams so that the two sub beams focus on the optical disc 4 before and after the optical axis. The diffraction grating surface is formed at a position where the return light from the optical disk 4 does not pass through the diffraction grating surface again when it enters the first diffraction element 13 again.

For this reason, the forward laser beam Lf is separated by the diffraction element 13 into a main beam and two sub beams. Of these beams, the main beam is used as laser light for signal reproduction (laser light for signal reproduction), and the two sub-beams are used as laser light for tracking error detection (laser light for tracking error detection).

The laser beam for signal reproduction and the two laser beams for tracking error detection reach the second diffraction element 14. The second diffraction element 14 determines the zero-order diffraction efficiency in the optical path where the three laser beams reach the optical disc 4,
Is set so that the product of the first order diffraction efficiency and the first-order diffraction efficiency in the optical path from the light-receiving element 3 to the signal reproducing light-receiving element 3 is maximized. The diffraction grating surface formed on the second diffraction element 14 is substantially parallel to the diffraction grating surface of the first diffraction element 13.

Of the three laser beams, the second diffraction element 1
The light component (0th-order diffracted light) transmitted through the light source unit 10
After being emitted from the optical disk and bent at a right angle by the rising mirror 18, the light is focused on the recording surface of the optical disk 4 via the objective lens 12. At this time, the laser beam for signal reproduction focuses on the recording surface, and the two laser beams for tracking error detection enter a front focus state and a rear focus state.

The three laser beams converged on the recording surface of the optical disk 4 are reflected there and become return light Lr traveling from the optical disk 4 to the light receiving element 3 for signal reproduction. These return lights Lr are again transmitted to the objective lens 12 and the rising mirror 1.
The light is incident on the second diffraction element 14 of the light source unit 10 through the light source 8.

Here, the second diffraction element 14 has only a function of diffracting each return light in a direction parallel to the substrate surface 111 of the semiconductor substrate 11, in this example, in the width direction of the package 20. There is no function of performing wavefront conversion such as focusing and diverging on each return light Lr. For this reason, the three return lights Lr incident on the second diffraction element 14 are diffracted by the diffraction action of the diffraction element 14 to change the traveling direction. That is, each return light Lr is diffracted and separated from the forward laser light Lf from the semiconductor laser light source 2A.

The light diffracted by the second diffraction element 14 is the first light
Incident on the diffraction grating 13. As described above, the diffraction grating surface of the first diffraction grating 13 is not formed in a range where these diffracted lights enter. For this reason, each diffracted light incident on the diffraction grating 13 passes through the first diffraction grating 13 and reaches the reflection mirror 15. These diffracted lights fall vertically by the reflecting mirror 15 and irradiate the respective light receiving surfaces of the signal reproducing light receiving element 3.

As shown in FIG. 7, the diffraction light of the return light of the laser light for signal reproduction forms light spots s1 and s2 on the light receiving surface A. Further, the diffracted light of the return light of the laser light for tracking error detection forms light spots s3 and s4 on the light receiving surfaces B1, B2 and C. The diffracted light of the return light of the other laser light for tracking error detection forms light spots s5 and s6 on the light receiving surfaces D1, D2 and E.

In this example, an RF signal is detected based on the amount of light received on the light receiving surface A of the light receiving element 3 for signal reproduction. The TE signal is detected by calculating the difference between the sum S1 of the light reception amounts of the light receiving surfaces B1, B2, and C and the sum S2 of the light reception amounts of the light receiving surfaces D1, D2, and E. The FE signals are received on the light receiving surfaces B1, B2, E
Is obtained by calculating the difference between the sum S3 of the received light amounts of the light receiving surfaces and the sum S4 of the received light amounts of the light receiving surfaces D1, D2, and C. In addition,
These signals are transmitted to the lead frame 23 of the light source unit 10.
Is generated by a control device (not shown) electrically connected to the lead 232.

In the optical pickup device 1, a part Lf1 of the front laser beam Lf emitted from the front emission end face 2f of the semiconductor laser 2 directly irradiates the monitoring light receiving element 25 disposed in front of the front emission end face 2f. (See FIGS. 5 and 6). Feedback control of the laser light output (forward laser light output) of the semiconductor laser 2 is performed based on the output signal of the monitoring light receiving element 25. The feedback control is also performed by the above-described control device.

As described above, in the optical pickup device 1,
By directly detecting a part Lf1 of the forward laser light Lf to be controlled, the output of the forward laser light Lf is feedback-controlled. Therefore, as compared with the feedback control using the rear laser light emitted from the rear emission end face 2 b of the semiconductor laser 2, the output of the front laser light Lf is more accurately adjusted to the output suitable for recording / reproducing on the optical disk 4. Becomes possible.

Further, since a part Lf1 of the front laser light Lf is detected, it is not necessary to emit the rear laser light from the rear emission end face 2b of the semiconductor laser 2. That is, by increasing the reflectance at the rear emission end face 2b of the semiconductor laser 2, laser light (forward laser light) can be intensively emitted from the front emission end face 2f. Thus, the high-power front laser light Lf required for writing the optical disc 4 can be generated with a small driving current, and the power consumption of the semiconductor laser 2 can be suppressed low.

Further, since a part of the forward laser light Lf is directly detected, a new optical element for guiding the part to the monitor light receiving element 25 is not required. Therefore, the cost of the light source unit 10 does not increase, and the assembling work of the optical element does not become complicated.

Further, in the optical pickup device 1,
Objective lens 1 using laser light for tracking error detection
2 is generated, so that the second diffraction element 14 that diffracts and separates the return light from the optical disc 4
A device having only a simple optical path separation function is employed.
In such a diffraction element 14, the diffraction pattern can be simplified. For example, the diffraction pattern can be linear. The diffraction element having such a diffraction pattern can reduce the degree to which the diffraction characteristics are deteriorated due to the wavelength fluctuation of the forward laser beam Lf, the displacement of the mounting position of each optical element, and the like. Therefore, the operation of the optical pickup device can be stabilized. In addition, since it is only necessary to produce a simplified diffraction pattern, the tolerance for the production error of the diffraction pattern can be increased,
The manufacturing cost of the diffraction element can be reduced.

Here, in the optical pickup device 1, the second
The diffractive element 14 has a function of diffracting the return light from the optical disc 4, and does not have a function of wavefront conversion. Therefore, the optical path length from the semiconductor laser 2 to the second diffraction element 14 is equal to the optical path length from the second diffraction element 14 to the signal reproducing light receiving element 3. As a result, the optical path length of the return light can be made shorter than before, and the optical system of the optical pickup device can be made compact. As a result, the size of the device can be reduced.

More specifically, since the second diffractive element 14 has a function of diffracting the return light and has no function of converting the wavefront, the convergence point of the light diffracted by the diffractive element 14 is
It is optically conjugate with the virtual light emitting point of the semiconductor laser 2 and the two tracking error detection laser beams divided and generated by the first diffraction element 13. Therefore, the following relationship is established between the emission point of the forward laser light Lf of the semiconductor laser 2 and the center of the signal reproducing light receiving element 3.

As shown in FIGS. 8 and 9, the thickness of the heat sink 24, the height from the surface where the heat sink 24 contacts the semiconductor laser 2 to the light emitting point O, the second diffraction element 14 at the wavelength of the semiconductor laser 2, And the optical distance along the optical axis Lu of the laser beam Lf between the semiconductor laser 2 and the diffraction grating surface of the second diffraction element 14 are represented by ts, hLD, θbs, and dbs, respectively. I do.
With this definition, the XZ coordinate of the center of the signal reproducing light-receiving element 3 when the light-emitting point O in the (X, Z) plane where the signal reproducing light-receiving element 3 is formed is defined as Equation (1). And (2).

X = dbs × sin (θbs) (1) Z = dbs × {1−cos (θbs)} + ts + hLD (2) The diffraction of the semiconductor laser 2 and the second diffraction element 14 As can be seen from FIG. 8, the optical distance of the forward laser beam Lf along the optical axis Lu to the grating plane is a position slightly shifted from the light incident surface of the second diffraction element 14 toward the semiconductor laser 2. This corresponds to the distance from the semiconductor laser 2. FIG.
9 and FIG. 9, the reflection angle of the reflection mirror 15 is 45 degrees.
In this case, the angle is set to degrees, and the deviation of the reflection angle of the mirror 15 and the angle deviation around the optical axis are not taken into consideration.

(Other Embodiments) Although the optical pickup device 1 uses the first and second diffractive elements 13 and 14 which are independent from each other, the first diffractive element 13 is provided on one surface. Of course, a single optical element having optical characteristics and having the optical characteristics of the second diffraction element on the other surface may be employed.

Further, a configuration in which the semiconductor laser light source 2A is mounted on the substrate surface 111 of the semiconductor substrate 11 is adopted.
The semiconductor laser light source 2A is connected to the stage 231 or the lead 232.
It is good also as a structure mounted in.

Further, the optical system of the optical pickup device 1 includes not only the optical element shown in FIG. 1 but also a lens for converting the laser beam Lf into a parallel beam, and a beam diameter of the laser beam in two orthogonal directions. An optical element such as a beam shaping prism for alignment, an aperture limiting means for reading the upper side of an optical disc of a different specification, or a wavelength-selective optical element may be included.

[0063]

As described above, according to the present invention, the monitoring light receiving element is formed on the substrate surface of the semiconductor substrate, and the monitoring light receiving element is positioned in front of the front emission end face of the semiconductor laser. The semiconductor substrate is set in the package of the light source unit. Further, the forward laser light from the semiconductor laser is made to directly enter the monitor light receiving element. According to the feedback control of the laser light output of the semiconductor laser having this configuration, the output of the forward laser light is surely adjusted to an output suitable for recording / reproducing on the optical recording medium, as compared with the feedback control using the rear laser light. be able to.

Since it is not necessary to emit the rear laser light, it is possible to emit a high-output front laser light with a small driving current by increasing the reflectance at the rear emission end face of the semiconductor laser. Further, there is no need to install a new optical element in the package for this feedback control.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical system of an optical pickup device to which the present invention has been applied.

2A is a schematic configuration diagram of a light source unit, FIG. 2B is a cross-sectional view taken along line AA ′ of FIG. 2A, and FIG. 2C is a cross-sectional view taken along line BB ′ of FIG. .

FIG. 3 is a front view of the light source unit shown in FIG.

FIG. 4A is a plan view of a package body which is a component of the package of the light source unit, and FIG.
FIG. 4C is a cross-sectional view taken along line D ′, and FIG. 4C is a cross-sectional view taken along line EE ′ in FIG.

FIG. 5 is an enlarged perspective view showing a semiconductor substrate and its peripheral portion in a light source unit of the optical pickup device.

FIG. 6 is an enlarged plan view showing a substrate surface of a semiconductor substrate in the light source unit of the optical pickup device.

FIG. 7 is an enlarged plan view showing a light-receiving element for signal reproduction in a light source unit of the optical pickup device.

FIG. 8 is a diagram for explaining a formation position of a light receiving element for signal reproduction in a width direction of a package in a light source unit of the optical pickup device.

FIG. 9 is a diagram for explaining the formation position of a light-receiving element for signal reproduction in the light source unit of the optical pickup device in the front-rear direction of the package.

[Explanation of symbols]

 Reference Signs List 1 optical pickup device 2A semiconductor laser light source 2 semiconductor laser 3 signal reproducing light receiving element 4 optical disk 10 light source unit 12 objective lens 13 first diffractive element 14 second diffractive element 15 reflecting mirror 20 package 21 package body 22 package cover plate 24 Heat sink 25 Monitor light receiving element 50 Light guide system 201 Cylindrical projection 203 Light passage hole Lf Forward laser light Lf1 Part of forward laser light

Claims (6)

[Claims] 1. A semiconductor laser, a separating element for separating forward laser light emitted from a forward emission end face of the semiconductor laser into laser light for signal reproduction and laser light for tracking error detection, Focusing means for focusing the tracking error detection laser light on the optical recording medium, a signal reproducing light receiving element for detecting return light from the optical recording medium, and forward laser light emitted from the semiconductor laser And a light guide system for guiding the return light to the signal reproducing light receiving element. The semiconductor laser, the signal reproducing light receiving element, and the monitor The light receiving element is built in a common package and integrated as a light source unit, and the light guide system transmits the return light from the semiconductor laser. In the optical pickup device including a diffraction element that diffracts and separates from the forward laser light, the light source unit includes, in the package, a semiconductor substrate including a substrate surface on which the monitor light receiving element is formed; An optical pickup device, wherein a monitoring light receiving element is arranged in front of the front emission end face of the semiconductor laser, and a part of the front laser light is directly incident on the monitoring light receiving element. 2. The optical pickup device according to claim 1, wherein the light receiving element for signal reproduction is formed on the substrate surface of the semiconductor substrate. 3. The optical pickup device according to claim 2, wherein an optical path length from the semiconductor laser to the diffraction element is equal to an optical path length from the diffraction element to the signal reproducing light receiving element. 4. The optical pickup device according to claim 3, wherein the semiconductor laser is mounted on an upper surface of a heat sink provided on the substrate surface of the semiconductor substrate. 5. The optical pickup device according to claim 1, wherein the focusing error is detected by using the tracking error detecting laser light. 6. A light source unit for an optical pickup device according to claim 1.